How to Measure the Thermal Stability of Eudragit®Standard ASTM E2550-11 describes the method of measuring the thermal stability of materials by means of thermogravimetry. As an example, let us determine the thermal stability of Eudragit® L100-55 (Evonik Industries). To this end, you need a thermobalance to measure the mass loss of your sample during heating until thermal decomposition. The TGA measurement was carried out using the following instrument and parameters:
- Instrument: NETZSCH TG 209 F1 Libra thermobalance coupled to the FT-IR System by Bruker Optics
- Sample: Eudragit® L100-55 (Evonik Industries)
- Sample mass: 7.33 mg
- Crucible: open aluminum oxide
- Temperature program: Heating to 600°C at 10 K/min
- Atmosphere: N2 (40 ml/min)
Thermal Stability With TG-FT-IR MeasurementsFigure 1 depicts the mass changes of Eudragit® L100-55 between 40°C and 600°C. The first mass-loss step of 0.8% up to 100°C indicates the release of surface water.
Water release or decomposition start?
The second mass loss of 5.9% at 200°C (DTG peak) is associated with the release of:
- Crystal water;
- CH2 and CH3 molecules (bands in the range 3000-2800 cm–1 and above 1000 cm–1).
The Decomposition Goes On…The peak at 294°C in the DTG curve is associated with yet another step in the decomposition process: the release of carbon dioxide and probably ethanol (figures 3 and 4). This can be explained by the splitting of an ester group off the Eudragit® molecule. The last and main decomposition step, with a mass loss of 88.5%, occurs at 393°C (DTG peak temperature). The characteristic bands of:
- carbon dioxide
- carbon monoxide (2300 cm-1 to 2100 cm-1)
- ester substance (band at 1749 cm-1)
- parts of the carbon Backbone (bands at 1460 cm-1 and 1380 cm-1)